Olgica Milenkovic Emina Soljanin P. Whiting Asymptotic Spectra of Trapping Sets in Regular and Irregular LDPC Code Ensembles. 39-55 2007 53 IEEE Transactions on Information Theory 1 http://dx.doi.org/10.1109/TIT.2006.887060 db/journals/tit/tit53.html#MilenkovicSW07